1. Field of the Invention
The present invention relates to a method for controlling a paging transceiver. More specifically, it relates to a method for maintaining a given output power level by compensating for changes in the output power level resulting from variations of frequency and temperature.
2. Description of the Related Art
FIG. 1 is block diagram showing the construction of a general paging transmitter. The output control of the paging transmitter as depicted in FIG. 1 is generally performed as follows. A transmission signal modulated in a modulator 2 is transmitted through antenna 10 after the output is amplified in a power amplifier unit 4. A power detect unit 6 positioned between the power amplifier unit 4 and the antenna 10 detects the output(power) of the RF signal outputted in a final terminal of the paging transmitter. Power detect voltage (PDV) is generated by converting the output of power amplifier unit 4 into the direct current in the power detect unit 6. The PDV is then applied to a main control unit 8. Also, a temperature detect voltage (TDV) is generated by converting the current temperature for the output of power amplifier unit 4 into the direct current in power detect unit 6. The TDV is then applied to the main control unit 8. The power detect voltage PDV and the temperature detect voltage TDV are transmitted to an A/D converter of the main control unit 8 where the respective analog voltage signals are converted into digital data which is applied to an internal processor.
The internal processing performed by main control unit 8 is illustrated in FIG. 2. FIG. 2 is a flow chart showing conventional RF power control operations in a paging transmitter. The internal processor installed within the main control unit 8 checks at step 100 whether or not the RF signal is under outputting. Thus, when determined that the RF signal was under outputting, the processor detects the power detect voltage PDV and the temperature detect voltage TDV applied from the power detect unit 6 as the digital data. Thereafter, the processor proceeds to step 102, and searches for current power of the RF signal and the temperature thereof in a matching table contained in the memory. The current power of the RF signal and temperature thereof is determined on the basis of the power detect voltage PDV and the temperature detect voltage TDV. The searched power and temperature is displayed as output data to an operator. The processor then compares the output data (the power value of the RF signal) with the preset operation power data at step 104. When the power data is different from the preset data thereas, the processor increases/raises or lowers the power control voltage PCV by using a D/A converter. That is, when the preset operation power data is more than the current power, the processor increases the power control voltage PCV at step 106. However, when the preset operation power data is less than the current power, the processor lowers the power control voltage PCV at step 108. In accordance with this, the power at the final terminal of the transmitter can be increased or lowered in relation to the power control voltage PCV. Thus, the power voltage applied to main control unit 8 is also varied, and the processor takes the loop and repeats the above operations until the digital data of the voltage is equal to the preset operation power value.
A method for controlling the RF power at the paging transmitter according to the prior art as described above is performed through easily controlling the RF power of the single frequency at the normal temperature. However, when the paging transmitter is used at the wideband frequency range (i.e., over 100 MHz) and over a wide temperature range (-30.about.+60.degree. C.), the power control value of the paging transmitter at the specific frequency and temperature differs greatly from the power meter directive value as dictated in the real power meter.
The following tables 1-3 show these differences. Table 1 shows the effect of varying frequencies on the main control unit directive value and the power meter directive value. Table 2 shows the effect of varying temperature on the main control unit directive value and the power meter directive value, and table 3 shows the effect of frequency and temperature variation on the main control unit directive value and the power meter directive. With reference to tables 1-3, the main control unit directive value and the power meter directive value change in response to the variation of frequency in the wideband frequency range (over 10 MHz) and the temperature variation at wide temperature range (-30.about.+60.degree. C.).
TABLE 1 ______________________________________ power meter directive value 928 Mhz 936 Mhz 944 Mhz main control unit (normal (normal (normal directive value temperature) temperature) temperature) ______________________________________ 300 watt 293 300 305 290 watt 285 291 295 280 watt 275 280 283 270 watt 263 269 273 260 watt 253 260 265 250 watt 245 250 255 ______________________________________
TABLE 2 ______________________________________ power meter directive value high normal low main control unit temperature temperature temperature directive value [936 MHz] [936 MHz] [936 MHz] ______________________________________ 300 watt 270 300 330 290 watt 261 291 321 280 watt 250 280 310 270 watt 243 269 303 260 watt 233 260 291 250 watt 225 250 281 ______________________________________
TABLE 3 ______________________________________ power meter directive value 936 MHz, main control unit 928 MHz, high normal 944 MHz, low directive value temperature temperature temperature ______________________________________ 300 watt 263 300 335 290 watt 256 291 328 280 watt 245 280 313 270 watt 236 269 306 260 watt 225 260 298 250 watt 220 250 288 ______________________________________
FIG. 4 is a graphical chart showing the comparison characteristics of a control unit directive value of RF power and a power meter directive value thereof as a function of frequency and temperature according to the prior art paging transmitter.